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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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230

COMPLEX BRASSES

2.  Determination of the Lead.—The liquid freed from metastannic
acid, or the original solution if the alloy does not contain tin, is evaporated
on a sand-bath with 5 c.c. of dilute sulphuric acid (i vol. acid to i vol.
water) until copious white fumes are emitted.    When cold, the residue
is heated gently and stirred with 50 c.c. of water to dissolve the basic sul-
phates of copper, zinc, etc., and the solution, after cooling, mixed with
15 c.c. of 95% alcohol.   After standing for 1-2 hours, the lead sulphate
which separates is collected in a Gooch crucible and is washed first with
a mixture of 60 c.c. water, 10 c.c. of alcohol and 0-5 c.c. of sulphuric acid
and then with alcohol until the reaction is neutral; it is then dried, heated
and weighed :  PbS04 X 0-6831 = Pb.

3.  Determination of the Copper.—The filtrate is evaporated almost
to dryness to eliminate the alcohol, the residue being diluted with water to
150 c.c. and electrolysed at the ordinary temperature.    Cathode, Winkler
electrode;  anode, spiral;  ND100 = o-r-o-2 amp. ;  voltage,  1-7-2 ;   dura-
tion, 15-16 hours.

During the whole course of the electrolysis, the voltage at the terminals
should never exceed 2, so that it is advisable to use a single accumulator
or a battery of accumulators joined in parallel. At the completion of the
deposition, the electrolytic beaker is lowered slowty and the electrodes
washed as they emerge. The washing of the cathode is completed with
water, alcohol and ether, and the weight determined after drying at 70°.

4.  Separation  of the  Iron  and  Manganese.—The  spiral   anode,
which is covered with a black coating of manganese dioxide, is immersed
in the liquid from which the copper has been separated, this being heated
with addition of 3-4 drops of hydrogen peroxide until the manganese dioxide
is completely dissolved.   The spiral is withdrawn and washed, and the
solution concentrated to 30-40 c.c. and poured, little by little and with
shaking, into a solution of 10 grams of pure sodium hydroxide in 30-40 c.c.
of water contained in a platinum or porcelain dish.    The iron and the man-
ganese are precipitated as oxides, while the zinc and aluminium pass into
solution as sodium zincate and aluminate.    The liquid is heated to boiling,
diluted with boiling water and filtered, the filtrate being collected in a half-
litre beaker containing about 100 c.c. of 20% sulphuric acid and the filter
washed with hot water.   The oxides separated are dissolved in a little
dilute sulphuric acid containing a few drops of hydrogen peroxide and the
solution again poured into sodium hydroxide solution of the concentration
mentioned above, the latter being heated to boiling, diluted and filtered
and the filtrate collected in the same half-litre beaker as the other.

(a] DETERMINATION OF THE IRON. The ferric and manganese hydroxides
are redissolved in the least possible quantity of 10% sulphuric acid, a few
drops of hydrogen peroxide being added and the solution heated. The
greater part of the free acid is neutralised with ammonia and the solution
poured into a boiling solution of 6-7 grams of ammonium oxalate in a little
water; after addition of 5-6 c.c. of 2% hydrazine sulphate solution and
dilution to about 200 c.c., the liquid is electrolysed to determine the iron
(see Ferro-manganese, Electrolytic Analysis).

(J) DETERMINATION OF THE MANGANESE.   The liquid from which thetreated with an excess